canvas绘制五星红旗
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>canvas绘制五星红旗</title>
</head>
<body>
<canvas id="canvas" width="600" height="400"></canvas>
<script>
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// 绘制背景
var width=canvas.width;
var height=width*2/3;
ctx.fillStyle="red";
ctx.fillRect(0,0,width,height);
var maxR=0.15,minR=0.05; //0.15大五角星的半径，0.05小五角星的半径
var maxX=0.25,maxY=0.25; //大五角星的位置
var minX=[0.50,0.60,0.60,0.50]; //小五角星的X坐标
var minY=[0.10,0.20,0.35,0.45]; //小五角星的Y坐标
var ox=height*maxX,oy=height*maxY; //大五角星的中心坐标
drawStar(ctx,ox,oy,height*maxR,"#ff0",0); //绘制五角星
for (var idx = 0; idx < 4; idx++) {
var sx = minX[idx] * height, sy = minY[idx] * height;
var theta = Math.atan((oy - sy)/(ox - sx));
drawStar(ctx,sx, sy, height * minR, "#ff0",-Math.PI/2+theta);
}
/*五角星的坐标为（sx,sy）,半径为radius,rotate为0时一个顶点在对称轴上*/
/*rotate:绕对称轴旋转rotate弧度*/
function drawStar(ctx,sx,sy,radius,color,rotate){
ctx.save();
ctx.fillStyle=color;
ctx.translate(sx,sy); //移动坐标原点
ctx.rotate(Math.PI+rotate); //Math.PI等于圆周率3.14
ctx.beginPath();
//360度分成5份，2/5*PI,但底下是PI/5*4
var dig=Math.PI/5*4;
for(var i=0;i<5;i++){ //画五角星的五条长边
var x=Math.sin(i*dig); //点的x坐标
var y=Math.cos(i*dig); //点的y坐标
ctx.lineTo(x*radius,y*radius);
}
ctx.closePath();
ctx.strokeStyle = "red"
ctx.stroke();
ctx.fill();
ctx.restore();
}
</script>
</body>
</html>
http://www.360doc.com/content/16/0809/10/10978981_581855158.shtml
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